Patent GB-903152-A (GB)
Title: Course guidance system
IPC: G05D1/02
Filed: 1959-01-02
Abstract: 903,152. Electric analogue calculating. STANDARD TELEPHONES & CABLES Ltd. Jan. 2, 1959 [Jan. 6, 1958], No. 183/59. Class 37. [Also in Group XL (c)] In a system for indicating on an aircraft its deviation from a desired straight course 1, Fig. 3, of magnetic bearing # means are provided for: (1) determining the instantaneous distance r and magnetic bearing # of a known form of radio beacon A, e.g. a Tacan beacon, from the craft and for computing the component L<SP>1</SP> = r sin (# - #) of the distance r perpendicular to the direction # of the course line; (2) computing the perpendicular distance L=r 0  sin (# - # 0 ) of the beacon from the course line 1 where r o  and # 0  are the known distance and bearing of the beacon from a reference point on the course line, e.g. the initial position O of the craft; and (3) determining the difference between L and L<SP>1</SP> to give the required deviation. The plan range r is computed from the measured slant range p and the difference between the heights H and H b  of the aircraft and the beacon. If the direction # of the course line is not known it may be computed from the known values r 0 , # 0 , and the values p f , # f  corresponding to a known position of the craft on the course. An additional computer is provided which in response to p, #, the heading γ and air speed V a  computes the magnitude V w  and direction # W  of the wind. If either of the # or # signals fail the wind computer operates in reverse in a " memory " mode as a dead reckoning computer and computes p and # as a function of V a , γ and the last computed wind values V w  and # w . If the course line extends through a plurality of adjacent or overlapping beacon coverage zones, Fig. 1 (not shown), manual or automatic means may be provided for tuning the craft receiver 4, Fig. 4, to the beacon on entering its zone and for setting in the data r 0 , # 0 , corresponding to said beacon. If there is a gap between adjacent zones, the system will operate in the memory mode when the craft is traversing the gap. Deviation computer, Fig. 4.-If the direction # of the course line is known the ganged switches 27 . . . 30 and clutches 5, 23 and 24 are in the positions shown. Shaft rotations proportional to 0 and # 0  produced respectively by the craft receiver 4 and a manual control 9 are applied to differential gears 6 and 8 together with a common input from the manual control 7 to give outputs (# - #) and (# - # 0 ) which control the settings of resolvers 10 and 11. A.C. voltages of opposite phase and of amplitudes proportional to r and r 0  are produced by potentiometers 12 and 16 and applied to the resolvers 10 and 11, respectively, to give outputs L<SP>1</SP>= r sin (# - #) and L=r o  sin (# - # 0 ) which are' combined differentially in a phase-sensitive circuit 20 to give an output indicative of the magnitude and sense of the deviation which is displayed on an indicator 21. The potentiometer 16 is set by the manual control 17 and the potentiometer 12 is controlled by a servomotor 43 in the plan range computer 13. A.C. voltages of opposite phase and of amplitudes proportional to the heights H and H b  of the craft and beacon are produced respectively by the altimeter 37 and the manually set potentiometer 39 and are combined in an amplifier 40 to give a resultant (H - H b ). An A.C. voltage proportional to the slant range p is produced by the receiver 4 and applied across the series combination of a potentiometer 42 and a capacitor 41. The phase of the voltage p is controlled so that the resultant voltage across the capacitor 41 which is also applied to the amplifier 40 is of opposite phase to the voltage (H-H b ) and the output from the amplifier 40 controls the servomotor 43 which adjusts the potentiometer 42 until the voltage across the capacitor 41 is equal in amplitude to the voltage (H-Hb); when this obtains the voltage across the potentiometer 42, and hence the position of the servomotor 43, is proportional to the plan range r. In order to compute #, the values p f  and # f  corresponding to the other known position r f , # f  on the course line are set in manually by controls 31, 33 and the switches 27-30 are set to position F, thereby disengaging the clutch 5, engaging the clutches 23 and 34, applying the quantity p f  to the plan range computer 13 in place of p and applying the quantities # f  and r f  to the differential gear 6 and resolver 10 in place of # and r. The computer now functions in a similar manner to its previous mode of operation but the course angle input # is now varied by a servomotor 22 in response to the output from the differential circuit 20 until said output is zero. Wind computer, Figs. 5, 6A and 6B. Under normal conditions when the receiver 4 is receiving p and # signals from a beacon the relay solenoid 67, Fig. 6B, is de-energized and hence the switches 51-66 are in position N, clutches 78 and 88 are engaged and clutch 99 is disengaged as shown in Figs. 6A and 6B. When the receiver 4 fails to receive either the p or # signals, the A.G.C. voltage increases and energizes the solenoid 67, thereby changing switches 51-66 to the M position, disengaging clutches 78, 88 and engaging clutch 99. In the normal (N) mode of operation shaft rotations proportional to # and # are produced by servo loops 44-and 68, respectively, whose inputs are coupled respectively to the # synchro 46 and the p voltage output in the receiver 4. Voltages proportional to b and p are also produced by generators 47 and 72 coupled to the servomotors in the servo loops 44 and 68. The voltage # is multiplied by p by means of a potentiometer in the circuit 70 controlled by the mechanical p signal and the voltages p and ## corresponding to the components of the ground speed Vg along and perpendicular to the instantaneous bearing # of the beacon are applied to a resolver 74 controlled by a servomotor 77 which adjusts the resolver until the output p sin # - ## cos # from one rotor winding R2 is zero; when this obtains the angular setting # of the rotor is equal to the angle #, Fig. 5, between the ground speed vector Vg and the direction of the beacon and the output p cos #+ p# sin # from the other rotor winding R1 is equal to the ground speed Vg. The voltage Vg is applied to a resolver 82 giving outputs Vg cos # and Vg sin 8, where # is the drift angle, i.e. the angle between the heading and the ground speed vector, and is obtained as the output from a differential gear 79 to which are applied (1) the angle #= (# - γ - #) from the servomotor 77 and (2) the angle (# - γ) from a differential gear 50 having inputs # and γ from the # servo loop 44 and heading transducer 80. The voltage Vg ces # from the resolver 82 is combined in a circuit 83, Fig. 6B, with a voltage V a  from the air speed transducer 84 to give a resultant (Vg cos # - V a ) which is applied together with the voltage Vg sin # to a resolver 85 controlled by a servomotor 87 which adjusts the resolver until the output (V g  cos # - V a ) sin # d  - V g  sin # cos # d  from one rotor winding R2 is zero; when this obtains the angular setting of the rotor is equal to the angle # d , Fig. 5, between the air speed and wind speed vectors V a  and V w  and the output (Vg cos 8 - V a ) cos # d +V d  sin # sin # d  from the other winding R1 is equal to the wind speed V w . The wind speed voltage V w  is converted by means of a servo 92 into a corresponding shaft rotation which controls the wind speed indicator 94 and a wind speed potentiometer 95. The angle # d  is combined with the heading angle γ in a differential gear 89 to give the wind direction # w  which is displayed by an indicator 90. In the memory (M) mode of operation the resolvers 85, 82 and 74 operate in a manner opposite to that described during the normal mode. A voltage representing the last computed wind speed V w  is applied from the potentiometer 95 to the rotor R1 of resolver 85 whose angular setting is controlled by the # d  output from the differential 89 and outputs # and ## are obtained from the stators S2 and S1 of resolver 74. The # output is integrated by the # servo loop 68 to give a shaft rotation representing # and the ## output is divided by the signal in the circuit 70 to give an electrical # signal which is integrated in the # servo loop 44 to give a shaft rotation representing #.